The subject matter disclosed herein relates to ultrasonic measurement devices and methods.
Ultrasonic inspection devices can be used to examine objects in order to measure various dimensions of structures and surfaces in the objects. These ultrasonic devices allow an inspection technician to maneuver an ultrasonic probe at or near the surface of the object in order to perform measurements of the object such as its thickness. Ultrasonic inspection devices and techniques are particularly useful in some industries, e.g., aerospace, power generation, and oil and gas transport or refining (e.g., pipes and welds), where inspection of test objects must take place without removal of the object from surrounding structures, and where interior structures of the objects cannot be measured through visual inspection. When conducting ultrasonic measurement, ultrasonic pulses or signals are emitted from ultrasonic transducers mounted in the ultrasonic probe and pass into a test object. As the ultrasonic signals pass into the object, various ultrasonic reflections called echoes, or echo sequences, occur as the ultrasonic signals interact with exterior and interior surfaces of the test object and are reflected back toward the ultrasonic probe. Large amplitude echoes among the reflected echoes are typically caused by emitted ultrasonic signals reflecting off of exterior and interior surfaces of the test object. These echoes are detected by the ultrasonic transducers in the probe and are analyzed by processing electronics connected to the ultrasonic transducers.
The amplitude and firing sequence of the ultrasonic transducers in the probe can be programmably controlled. The resulting ultrasonic echoes are recorded as echo data by the processing electronics, and include amplitudes and delay times. By tracking the time difference between the emission of the ultrasonic signals and the receipt of the echo data, i.e., the time-of-flight, and measuring the amplitude of the received echo data, various characteristics of a test object can be determined such as, e.g., depth, size, orientation, and thickness. Accordingly, the accuracy of this measurement hinges on the precision of the amplitude and delay resolution achieved with respect to the received echo data. Surfaces and structures of test objects are represented in the return echo sequences as maximum amplitude peaks. Therefore, the magnitude of positive or negative maximum peaks in the echo sequences must be precisely determined, as well as the delay time associated therewith, for accurate measurements to be made.
In an ultrasonic testing device, maximum amplitude peaks are detected by first defining time intervals, i.e. gates, for evaluating received ultrasonic echoes. For each gate a peak value memory detects and records the maximum of the ultrasonic echo detected during the time interval. These gates have a fixed position and width, which are selected according to expected detected thickness ranges and tolerance values. Thus, for a test object having rapidly varying thicknesses to be measured, the maximum threshold within a time interval can be easily exceeded, and so cannot be precisely evaluated. Typically, the echo sequence received at the ultrasonic probe is digitized and stored as echo data immediately after reception. The amplitudes and delay times of the echo sequence are then determined from the stored digital echo data. The accuracy obtainable from using high-frequency ultrasonic signals is limited by the performance of the analog/digital converter (ADC) used, which is determined for the most part by its sampling rate, or sampling frequency, and its bit length. The lower the ratio of sampling frequency to the emitted ultrasonic signal frequency, the poorer the resolution of the amplitude and delay determination. High sampling rate ADCs and associated higher speed memory modules can be prohibitively expensive. If commercially available ADCs and standard memory modules are used, the sampling density of the ultrasonic echo sequences is not sufficient for precise determination of the magnitude of maximum amplitude peaks and their associated delay times.
The gating method described above is not adequate for measuring very small wall thicknesses because the time-of-flight values for the received ultrasonic echo data are short compared to the duration of an emitted ultrasonic pulse. Also, the fixed gate position cannot capture the actual variation of the time-of-flight values of received ultrasonic echoes in such a tolerance range. As mentioned above, rapidly varying wall thickness is another situation where the ultrasonic signal gating method is not adequate for accurate tracking One method of addressing these shortcomings has involved splitting the ultrasonic echo receiving circuit into a plurality of overlapping ADC's to increase its dynamic range and to overcome the need for pre-setting the gates which limits their overall range.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.